1. Field of the Invention
The present invention relates to an apparatus for dressing a polishing pad used in polishing a workpiece, such as a semiconductor wafer, and more particularly to a dressing apparatus provided in a polishing apparatus for polishing the workpiece to planarize a surface thereof. The present invention also relates to a chemical mechanical polishing apparatus and a chemical mechanical polishing method using such a dressing apparatus.
2. Description of the Related Art
In recent years, semiconductor devices become smaller and smaller, and device structures become more complicated. A surface planarization is a very important process in fabrication of the semiconductor devices. A typical technique used in the surface planarization is chemical mechanical polishing (CMP). In the process of chemical mechanical polishing, a semiconductor wafer is brought into sliding contact with a polishing surface of a polishing pad, while a polishing liquid, containing abrasive grains such as silica (SiO2), is supplied onto the polishing surface, whereby a surface of the semiconductor wafer is polished. A fixed abrasive pad, which is constituted by abrasive grains bonded by a binder, may be used instead of the polishing pad.
The process of chemical mechanical polishing is performed using a CMP apparatus. Typical CMP apparatus includes a polishing table with a polishing pad attached to an upper surface thereof, and a top ring (also referred to as a carrier) for holding a substrate, such as a semiconductor wafer, which is a workpiece to be polished. The polishing table and the top ring are rotated about their own axes respectively, and in this state the top ring presses the substrate against a polishing surface (i.e., an upper surface) of the polishing pad at a predetermined pressure, while the polishing liquid is supplied onto the polishing surface, to thereby polish the substrate to a flat and mirror finish. The polishing liquid to be used is typically composed of an alkali solution and fine abrasive grains (e.g., silica) suspended in the alkali solution. The substrate is polished by a combination of a chemical polishing action by the alkali and a mechanical polishing action by the abrasive grains.
When the substrate is polished, the abrasive grains and polishing debris adhere to the polishing surface of the polishing pad. In addition, characteristics of the polishing pad change and its polishing capability is lowered. Therefore, as polishing of the substrate is repeated, a polishing speed (i.e., a removal rate) is lowered and uneven polishing occurs. Thus, in order to condition the polishing surface of the deteriorated polishing pad, a dressing apparatus is provided adjacent to the polishing table.
The dressing apparatus typically has a rotatable dresser head and a dressing member secured to the dresser head. The dressing apparatus is configured to press the dressing member against the polishing surface of the polishing pad on the rotating polishing table, while rotating the dresser head about its own axis, to thereby remove the abrasive grains and the polishing debris from the polishing surface of the polishing pad and planarize and condition (i.e., dress) the polishing surface. Generally, the dressing member to be used has diamond particles electrodeposited on a surface thereof (i.e., a dressing surface) to be brought into contact with the polishing surface.
There are two ways of dressing the polishing surface of the polishing pad using the above-described dressing apparatus: one is a way of dressing the polishing surface concurrently with polishing of the substrate; and the other is a way of dressing the polishing surface during an interval between the polishing processes of the substrates. In both ways, a certain amount of the polishing surface is scraped off by dressing. However, due to the complexity of generating a vertical and horizontal force toward a dresser when dressing, it is difficult to control a dressing load while avoiding an unacceptable fluctuation of an attitude of the dresser. The improvement of the apparatus for dressing a polishing surface has been awaited.